Tests and scans may come back clear, but it doesn't mean the pain isn't real.

There are many types of chronic pain that are known and probably many others that research hasn't discovered yet. One form of chronic pain is 'Pain Disorder' which is thought to be established purely by psychological means.

What Is Pain Disorder?

Pain Disorder is a form of chronic pain that is thought to be driven by psychological distress. Pain Disorder is complex both in its manifestation in the body and in its definition.

In basic terms, a person has Pain Disorder when all other avenues of diagnosis have been ruled out and the pain the person is experiencing is believed to be driven by psychological stress over anything else.

"When there is no clear mental illness driving the pain and when there is no clear physical cause that is driving it that is observable, then it falls under the pain disorder bracket," neuroscientist Dr Bernadette Fitzgibbon, a National Health and Medical Research Council fellow told HuffPost Australia.

Just because you can't see it in a scan or your can't make sense of it doesn't make it any less real for the individual who lives with it.

Fitzgibbon also says that it's important to note that Pain Disorder is not caused by mental illness, even though it currently sits under the mental health diagnostic criteria. If a person is experiencing pain driven by a mental illness, this pain will be diagnosed as part of that already existing problem. In fact, this is the case with any other diagnosis that might involve chronic pain, like Fibromyalgia or Arthritis. Where there is a definite diagnosis, the pain is classified as part of that disorder.

Pain Disorder is diagnosed when all diagnostic avenues have been exhausted. This doesn't necessarily mean that there isn't a psychological cause for the pain, it's just that researchers and clinicians may not understand where the pain in coming from at this stage. This is where the complexity of Pain Disorder's definition and cause comes into play.

What Causes Pain Disorder?

The cause of Pain Disorder itself is unclear, which forms part of the reason why people are diagnosed with it. While this is both ambiguous and confusing, using trauma as an example can help clarify how this type of chronic pain can develop and how there can be missing links between initial events in a person's life and how pain can then manifest elsewhere in the body.

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"When you look at something like trauma not everybody who has a trauma develops PTSD and not everyone who has a trauma has a chronic pain," Fitzgibbon explained.

"When it comes to pain there is a higher rate of people who have a history of trauma who have chronic pain later on. Now that doesn't necessarily mean that it is purely psychologically driven like a pain disorder might infer because having a trauma can execute your nervous system's response to stimuli that you are experiencing in day-to-day life.

"There is something that has happened in your life and your nervous system has responded to the psychological stress and it has responded in a way that has made it heightened, more responded, more reactive."

You need to have a multi-modality, a multi-disciplinary approach to treat persistent pain problems.

"The classic story we often hear is someone is having a rough trot at work and then they go and try and pick up a box at work and they do their back, they go on workers comp and suddenly their back injury --which every other Joe would be fine [with] -- suddenly one case of a little twinge of a back turns into a massive long term or back injury," Hutchinson told HuffPost Australia.

"The rates of pain in those people who have ongoing life problems are much higher than someone who isn't experiencing that."

So essentially, it is well established in medicine that there is a connection between trauma and chronic pain like Pain Disorder, however, the way in which these are connected remains unclear.

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People with on-going life problems are more likely to experience chronic pain.

"What is interesting is that the rates of persistent pain in boys and girls are almost identical. As soon as puberty kicks in, girls turning into women rapidly increase their rates of persistent pain so we know that there is a hormonal component to it."

As for Pain Disorder specifically, there are no exact numbers as to how many people have it, as it is so difficult to define.

How Is It Managed?

Pain Disorder is incredibly difficult to diagnose, as often evidence of the pain doesn't show up on scans or in tests. As there is no cure for Pain Disorder, the treatment focuses on managing the pain.

"You need to have a multi-modality, a multi-disciplinary approach to treat persistent pain problems," Hutchinson said.

Fitzgibbon also told HuffPost Australia that psychology can be a key way to manage Pain Disorder.

"They are treated in a variety of different ways and the stand out treatments would be Cognitive Behaviour Therapy where you are dressing someone's thinking profiles and trying to improve the way that they cope with incoming information," Fitzgibbon said.

Other treatment types like massage, mindfulness and medication can be used to ease the condition, while surgical solutions are used in last resort cases.

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CBT and mindfulness are two common treatments for Pain Disorder.

The fact is, chronic pain problems like Pain Disorder are serious medical conditions that affect a person's quality of life. Both Fitzgibbon and Hutchinson say that simply because scans or tests return clear, doesn't mean that the pain doesn't exist.

"The fear of treating or acknowledging the presence of a persistent pain when there is 'nothing' -- and I am doing air quotes here -- 'nothing' wrong with the person simply because a scan didn't come up positive. It doesn't gel with the modern understanding of where pain originates from," Hutchinson said.

"Pain itself is real with or without something to show it," Fitzgibbon said. "If somebody says they are in pain and they are feeling pain and that is real for them, then it is a real thing.

"Just because you can't see it in a scan or your can't make sense of it doesn't make it any less real for the individual who lives with it."